Enjoy the fun of physics with simulations!

Backup site http://enjoy.phy.ntnu.edu.tw/ntnujava/

Title: Noise abatementPost by: ronaldbolton1 on September 18, 2009, 08:23:27 pm
We are preparaing research on noise abatement for a planned law enforcement firing range. We would like to prepare some preliminary estimates before we begin our formal environmental study. The area is described as follows: The main range from which firing will take place is level and rectangular with a width of 300 feet and a length of 1000 feet. It stands at 165 feet above sea level. The firing direction is parallel with the long side (1000 feet), and there will be a 20 foot high by 300 foot wide main earthen berm at the end into which the shooter will fire. This berm will have a 45 degree slope which will face the shooter. The remaing three sides of the range perimeter will be surrounded by earthen side / end berms, sloping inward at 45 degrees (all berm heights are in addition to the stated ground height of 165 feet). We would like to model different heights (8, 12, and 20 foot heights) for the three earthen berms on the sides and end to see what is most effective in dispersing noise away from nearby residences. The main berm has a fixed height of 20 feet. There are groups of residences parallel to the sides of the rectangle at 1) a distance of 3050 feet away and at a height of 202 feet above sea level, 2) a distance of 2900 feet away at a height of 170 feet above seal level, and a distance of 3200 feet at 165 feet above sea level. Gun fire will take place at the center point widthwise, 150 feet away from the main berm, directed into the main berm. Fire will be by 40 handguns firing standard .40 caliber ammunition. What I need is an estimate of the decibel level at each of the groups of residences. I know this is kind of lengthy, but I think I've covered everything. Any help will be greatly appreciated.
Captain Ronald Bolton Northport, Alabama Police Department Title: Re: Noise abatementPost by: Fu-Kwun Hwang on September 19, 2009, 03:28:28 pm
The surface area from a point source is proportional to r
^{2}.If the distance is increase by 10 times, the surface area will increase 100 times. So the energy density will be reduced to 1/100. The sound level is measured in db: if the energy is reduced to 1/10, the sound level will be increase by 10 db. if the energy reduced to 1/100, the sound level will be increase by 10+10=20db. if the energy reduced to 1/1000, the sound level will be increase by 10+10+10=30db. Assume the gun fire is a point sound source, if you can measure the sound level at 30 feet away (assume it is 120db), then the sound level at 300 feet can be eastimated as 120-20=100db, and the sound level at 3000 feet can be eastimated as 120-40=80db. The sound level can be further reduced if sound can be reflected by a high enough wall. Title: Re: Noise abatementPost by: ronaldbolton1 on September 25, 2009, 02:18:47 am
Thanks!
This is just what I was looking for. I believe we can calculate everything out from here. Thanks again and have a great day. Ronald Bolton |